Abstract. In this paper, size and morphology of the grain refiner and modifier particles in the Al-3%B-3%Sr master alloy production by using different cooling rates were investigated. Two Al-3%B-3%Sr master alloys were produced with 0.2 and 10°C/s, respectively. The grain refinement and eutectic modification efficiency of the Al-3%B-3%Sr master alloy were tested in casting process of A356 alloy by addition of 4wt.% and holding times for 10-120 min. The experimental result showed that microstructure of the M1 alloy (Slow cooling) consisted of larger solidified particles of AlB2, SrB6 and Al4Sr in the matrix of α-Al compared to the M2 alloy (Rapid cooling). The addition of the M1 alloy in cast A356 alloy, it was found that small grain size and fully modify eutectic silicon were obtained from the holding time in a range of 10-60 min. While the addition of M2 alloy, a small grain size was achieved in shorter holding time in a range of 10-30 min but the eutectic silicon was partly modify. From the thermal analyzed result, solidification of un-modified A356 alloy was changed after addition of Al-3%B-3%Sr master alloy. It was clearly observed that both the undercooling of nucleation and eutectic reaction was reduced and the solidification time was shifted to longer.
The effects of the grain refinement and eutectic Si modification on tensile properties by using Al-B-Sr master alloys in A356 cast alloy were investigated. Two different master alloys, Al-4%B-1%Sr (4B1Sr) and Al-3%B-3%Sr (3B3Sr), were developed. In microstructure observation, the master alloys were consisted of AlB2, SrB6, AlSrF, KAlF4 and Al4Sr compounds. It should be noted that the α-Al phase also exists in two master alloy. The result showed that the AlB2 area fraction in the 4B1Sr alloy was higher than the 3B3Sr alloy. The 4B1Sr alloy has better efficiencies of α-Al grain refinement and eutectic Si modification than the 3B3Sr alloy, and α-Al grains are refined from 3035 to 312 μm and the eutectic Si is modified from the acicular to fibrous morphology. The tensile properties of 4 wt.% treated with 4B1Sr alloy has higher UTS and elongation compared to the treated with 3B3Sr alloy.
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